Conspectus
Porphyrin
derivatives are ubiquitous in nature and have important
biological roles, such as in light harvesting, oxygen transport, and
catalysis. Owing to their intrinsic π-conjugated structure,
porphyrin derivatives exhibit characteristic photophysical and electrochemical
properties. In biological systems, porphyrin derivatives are associated
with various protein molecules through noncovalent interactions. For
example, hemoglobin, which is responsible for oxygen transport in
most vertebrates, consists of four subunits of a globular protein
with an iron porphyrin derivative prosthetic group. Furthermore, noncovalently
arranged porphyrin derivatives are the fundamental chromophores in
light-harvesting systems for photosynthesis in plants and algae. These
biologically important roles originate from the functional versatility
of porphyrin derivatives. Specifically, porphyrins are excellent host
compounds, forming coordination complexes with various metal ions
that adds functionality to the porphyrin unit, such as redox activity
and additional ligand binding at the central metal ion. In addition,
porphyrins are useful building blocks for functional supramolecular
assemblies because of their flat and symmetrical molecular architectures,
and their excellent photophysical properties are typically utilized
for the fabrication of bioactive functional materials. In this Account,
we summarize our endeavors over the past decade to develop functional
materials based on porphyrin derivatives using bioinspired approaches.
In the first section, we discuss several synthetic receptors that
act as artificial allosteric host systems and can be used for the
selective detection of various chemicals, such as cyanide, chloride,
and amino acids. In the second section, we introduce multiporphyrin
arrays as mimics of natural light-harvesting complexes. The active
control of energy transfer processes by additional guest binding and
the fabrication of organic photovoltaic devices using porphyrin derivatives
are also introduced. In the third section, we introduce several types
of porphyrin-based supramolecular assemblies. Through noncovalent
interactions such as metal–ligand interaction, hydrogen bonding,
and π–π interaction, porphyrin derivatives were
constructed as supramolecular polymers with formation of fiber or
toroidal assembly. In the last section, the application of porphyrin
derivatives for biomedical nanodevice fabrication is introduced. Even
though porphyrins were good candidates as photosensitizers for photodynamic
therapy, they have limitations for biomedical application owing to
aggregation in aqueous media. We suggested ionic dendrimer porphyrins
and they showed excellent photodynamic therapy (PDT) efficacy.